U.S. Pat. No. 4,143,054 to Sprague discloses a method for preparing 7-oxabicycloheptane prostaglandin derivatives wherein maleic anhydride is made to react with an unsubstituted or substituted furan of the formula ##STR5## e.g., in ether solution at room temperature, to form a compound having the formula ##STR6##
Reduction of the compound of formula B, e.g., catalytically, for example, in the presence of palladium-carbon, provides a reduced product having the formula ##STR7##
The compound of formula C is then converted to a compound having the formula ##STR8## e.g., by reduction in tetrahydrofuran with a borohydride like sodium borohydride or zinc borohydride.
Treatment of the compound of formula D with diisobutylaluminum hydride or diisobutylborane yields a compound having the formula ##STR9## which then is submitted to Wittig reaction conditions e.g., with an (alkoxymethyl)triphenylphosphonium halide like (methoxymethyl)triphenylphosphonium chloride in the presence of an alkali metal alkylamide like lithium diisopropylamide, a lithium alkyl like n-butyl lithium in an inert organic medium like toluene, tetrahydrofuran or the like, at a temperature in the range of about -10.degree. to 25.degree. C.
This reaction produces a compound having the formula ##STR10##
The product of formula F is treated with an acid like formic acid or trifluoroacetic acid to yield a product having the formula ##STR11##
The compound of formula G is then used to form 7-oxobicycloheptane or heptene prostaglandin derivatives.